Intro to Controller Area Networks (CAN) Part 2 of 2, E. Zivi, April 1, 2015 References: 1.A CAN...
23
Intro to Controller Area Networks (CAN) Part 2 of 2, E. Zivi, April 1, 2015 chip Application Note AN00228a entation Guide Analog Devices Application Note AN-1123 ersion 2.0 , Siemens Microelectronics, Inc., October 98 ut-can/the-can-protocol.html otocol-tutorial/ w.can-cia.org/index.php?id=systemdesign-can-physicallayer Requirements , TI SLLA270–January 2008 er-solutions.co.uk/download/Peak/CAN-Tutorial.pdf tions.com/english/about_canopen/about_canopen.shtml ANopen , by Pfeiffer, Ayre and Keydel s to Industrial Networks , by Farsi and Barbosa puter Networks, Alan Mislove, Northeastern University p:// electrosofts.com/can/index.html
Intro to Controller Area Networks (CAN) Part 2 of 2, E. Zivi, April 1, 2015 References: 1.A CAN Physical Layer Discussion Microchip Application Note AN00228a
Intro to Controller Area Networks (CAN) Part 2 of 2, E. Zivi,
April 1, 2015 References: 1.A CAN Physical Layer Discussion
Microchip Application Note AN00228a 2.Controller Area Network (CAN)
Implementation Guide Analog Devices Application Note AN-1123
3.Controller Area Network, CANPRES Version 2.0, Siemens
Microelectronics, Inc., October 98
4.http://www.kvaser.com/en/about-can/the-can-protocol.htmlhttp://www.kvaser.com/en/about-can/the-can-protocol.html
5.http://www.kvaser.com/can-protocol-tutorial/http://www.kvaser.com/can-protocol-tutorial/
6.CAN physical layer ref:
http://www.can-cia.org/index.php?id=systemdesign-can-physicallayerhttp://www.can-cia.org/index.php?id=systemdesign-can-physicallayer
7.Controller Area Network Physical Layer Requirements, TI
SLLA270January 2008 8.CAN Tutorial,
http://www.computer-solutions.co.uk/download/Peak/CAN-Tutorial.pdfhttp://www.computer-solutions.co.uk/download/Peak/CAN-Tutorial.pdf
9.CANopen Introduction, ref:
http://www.canopensolutions.com/english/about_canopen/about_canopen.shtmlhttp://www.canopensolutions.com/english/about_canopen/about_canopen.shtml
9.Embedded Networking with CAN and CANopen, by Pfeiffer, Ayre and
Keydel 10.CAN open Implementation: Applications to Industrial
Networks, by Farsi and Barbosa 11.CS4700/CS5700 Fundamentals of
Computer Networks, Alan Mislove, Northeastern University
12.Controller Area Networks
http://electrosofts.com/can/index.htmlhttp://electrosofts.com/can/index.html
Slide 2
Review: CAN is the Nervous System of Many Complex Systems New
cars typically contain 50 to 100 microcontrollers
Slide 3
Review: CAN & International Standards Organization (ISO)
Open Systems Interconnect (OSI) Reference Model 3 High level CAN
Protocols implement Application layer and skip the four intervening
layers
Slide 4
In Future Classes Well Introduce The CANopen Application 4 High
level CAN Protocols implement Application layers and skip the four
intervening layers ISO 11898 CAN Data Link Layer ISO 11898 CAN
Physical Layer Application CiA 301 CANopen Application Layer &
Communication Profile CiA 302 CANopen Framework for CANopen
Managers & Programmable Devices CiA 4xx Device Profiles CiA 401
Generic I/O Profile CiA 402 Motion Control Profile IEC 61131-3
Programmable Devices Profile Not Implemented by CAN or CANopen
Slide 5
Review: CAN Differential Bus Interface Transceivers The CAN
idle state presents a recessive state, signaled by a small
differential voltage across CANH and CANL. With the indicated split
termination, this idle voltage will be halfway between VDD
(positive supply) and VSS (ground). The CAN dominant state occurs
when one or more transceivers simultaneously close the indicated
transistor switches driving CANH and CANL toward VDD and VSS,
respectively. This open collector transistor switch configuration
is referred to as a wired or since any node transmitting a dominant
bit always overrides a recessive bit. Since a dominant bit
represents a logic 0, this arrangement is sometimes referred to as
wired and since bus a logic 1 state is achieved only if all nodes
(node 1 AND node 2 AND node 3 ) signal logic 1 recessive bits).
Micro- controller Transceiver Additional Transceivers Transistor
Switches 60 Split Termination Example Capacitive coupling to ground
5
Slide 6
Review: CAN ISO11898 5V Nominal Bus Levels Assuming Split
Termination Recessive voltage 2.5V 6
Slide 7
Example CAN Sample Signaling 7 Dominant bus state = logic 0
Recessive bus state = logic 1
Slide 8
Review: Wired OR Closing Node A switch OR closing Node B switch
turns on the light. Conversely, the light is off unless Node A
switch is open AND Node B switch is also open. 8
Slide 9
Review: CAN Arbitration Animation Mouse over graphic to control
animated bus arbitration example 9
Slide 10
CAN Bit Synchronization, Timing & Propagation Delay 1.CAN
signaling is bit synchronized across the entire network during the
Sync portion which is the time required for each node to
synchronize with the leading edge of a recessive to dominant edge
transition. 2.The Signal Propagation is the time for the bit signal
to propagate throughout the network. 3.Longer networks result in
longer Signal Propagation delays which require longer bits
resulting in slower data rates. 4.The Phase 1 portion delays
sampling so that the bit signal can settle to a stable value Signal
Propagation Propagation delay Settling time Sample Point 10 Faster
bit rates require shorter propagation delays and therefore, smaller
networks.
Slide 11
CAN Bit Rate Versus Bus Length 11 For a CAN bus, the signaling
rate is determined from the total system delay down and back
between the two most distant nodes of a system and the sum of the
delays into and out of the nodes on a bus with the typical 5ns/m
prop delay of a twisted-pair cable. A conservative rule of thumb
for bus lengths over 100 m is: Signaling Rate (Mbps) Bus Length (m)
50 Bus Length (m) Signaling Rate (Kbps) 401,000 100500 200250
500100 100050
Slide 12
CAN Synchronization Via Bit Stuffing CAN nodes use Recessive to
Dominant edges to maintain bit synchronization. Bit Stuffing
ensures sufficient Recessive to Dominant edges to maintain bit
synchronization A stuff Bit inserted after 5 consecutive bits at
the same state A Stuff Bit is the inverse of previous bits and is
discarded by the receiver
Slide 13
Slide 14
MicroMod TPDO 2 Transmit on Analog In Change of State Message
(40 S / Division):
Slide 15
MicroMod Heartbeat, Note ACK bit transmitted by Receiving Node
(40 S / Division):
Slide 16
TPDO 2 Analog Input Transited on change of state 4 Words, 2
Bytes each, little endian PCAN-Diag Hand Held Diagnostic Scope (40
S / Div.) 10-bit Analog Input Conversion Factor 5 V / 1023 counts =
0.0048876 V / count 0x023b 571 10 2.791 V 0x017a 378 10 1.847 V
0x0174 372 10 1.818 V 0x0169 361 10 1.764 V
Slide 17
MicroMod Heartbeat, with ACK bit (40 S / Div.) CANopen
Heartbeat Messages 0: Boot-up 4: Stopped 5: Operational 127:
Pre-operational Heartbeat 1 Byte Node Status
Slide 18
Five Types of CAN Error Checking 1.Bit error: Transmitting node
compares transmitted & received bit value. 2.Stuff error: More
than 5 successive recessive or dominant bits without a Stuff Bit.
3.CRC error: Sender CRC value in message does not match receiver
CRC calculation. 4.Form error: Frame is not formatted properly.
5.Acknowledgement error: Transmitter sends recessive ACK bit. At
least one receiver node must assert a dominant ACK reply into
sender message.
Slide 19
The cyclic redundancy check (CRC) method is used for detection
of bit errors. The binary polynomial used in CAN 2.0 is: gCAN (x) =
x15 + x14 + x10 + x8 + x7 + x4 + x3 + 1 = 1100 0101 1001 10012 CAN
Cyclic Redundancy Check Bit Bucket Error Frame is a superposition
of 6 to 12 consecutive Bits asserted by nodes that detect an error.
Note that Error Frame breaks bit stuffing rules
Slide 20
CAN Example Physical Network Layout 20
Slide 21
Typical Differential CAN Cabling Differential signaling
minimizes common mode noise Twisting cables minimizes effects of
electromagnetic interference Optional cable shielding protects
against electrostatic interface 21
Slide 22
CAN Typical Physical Layer Connector CAN has a variety of
connectors for various applications. The sub-D connector, shown
above, is often used in laboratory setups. Only CAN_H and CAN_L are
required, the other signals are optional. Note that CAN cables can
distribute power to remote nodes. 22
Slide 23
Characteristic Impedance of CAN Twisted Cable Voltage charges
capacitance, current charges inductance as wave travels down
transmission line. Transmission line inductance & capacitance
Equivalent Circuit